Abstract

Skull, hyobranchial, and dental ontogeny of Onychodactylus fischeri (Hynobiidae) is described based on a developmental series ranging from early larvae to old postmetamorphic animals. If compared with other hynobiids (Ranodon sibiricus and Salamandrella keyserlingii), larvae of O. fischeri display the underdevelopment of certain larval specific features: e.g., the coronoid is edentate and occurs as a tiny bone only in the earliest larvae; the «Zahnfeld» on the vomer and palatine is absent, the palatine portion of the palatopterygoid is reduced. On the other hand, adult postmetamorphic O. fischeri specimens show the underdeveloped cranial and postcranial skeletal features in comparison with adult R. sibiricus and S. keyserlingii. Two phenomena seem to account for the abbreviation of the ontogenetic trajectory in O. fischeri. First, in O. fischeri which has the largest eggs among hynobiids, the initial larval development appears to have been shifted into the embryonic period (embryonalization which is accompanied in amphibians by the reduction or loss of certain larval specific features). Second, paedomorphosis caused by the retarded rate of somatic development in O. fischeri appears to have resulted in the loss or reduction of features that appear later in R. sibiricus and S. keyserlingii and, likely, in the ancestral ontogeny.